Myths vs facts: FT3 and Langlebigkeit

The claim that high FT3 levels directly promote longevity is a myth. The evidence is nuanced: thyroid hormones regulate metabolism, but epidemiological data show that both elevated and low FT3 in older adults are associated with increased mortality. Some observational studies suggest a U-shaped relationship, with moderate FT3 being optimal. However, these are associations, not causation. Reference ranges vary by lab and population. DTC tests often market FT3 as a 'longevity marker' without robust clinical backing. Fact: FT3 alone is not a reliable predictor of lifespan. More relevant are TSH, fT4, reverse T3, inflammatory markers, and lifestyle. Isolated FT3 measurement without medical context can mislead. Caution against unguided supplementation (e.g., T3 drugs) – they may increase risk of arrhythmias or bone loss. Evidence: mostly mechanistic and observational; no strong interventional trials.